1. Field of the Invention
The present invention relates to a linear actuator comprising a driven spindle having a nut which is connected to the expelling rod of the actuator. An actuator of this type is for instance known from EP-B1-0 531 247 and EP-A1-0 577 541. The invention also relates to a method of manufacturing the actuator.
2. The Prior Art
Linear actuators that, e.g., are used for raising and lowering movements on hospital beds can be relatively heavily loaded. For instance, an actuator can be loaded with up to 15000 N axially and torques to the size of 25 Nm.
The spindle, the expelling rod as well as the nut of the actuator are made of metal, and the nut is secured to the hollow expelling rod by threaded insertion into the inner thread of the rod and prevented against turning, e.g., by welding.
It is of upmost importance that the nut and the expelling rod are rigidly connected to each other, as the aforementioned axial and torque forces must be transferred from the nut to the expelling rod.
It is not enough that the forces must be transferred in a sufficiently secure manner; there are also in certain cases demands for low friction, life time lubrication, low noise level, low production and service costs. Linear actuators are attractive because they easily can be incorporated in an electrically control and also are relatively inexpensive.